1. Field of the Invention
The present invention relates to a solid-state laser system and, more particularly, to a solid-state laser system wherein the wavelength of a fundamental wave laser beam generated by a laser medium is converted by means of a non-linear optical element to obtain a higher harmonic frequency.
2. Description of the Related Art
First, an example of a conventional second harmonic generating solid-state laser system will be described below with reference to FIG. 5.
The second harmonic generating solid-state laser comprises a semiconductor laser 51 such as a laser diode (hereinafter referred to as "LD"), a condenser lens 52, a solid-state laser rod 53, a second harmonic generating non-linear optical element 54 (hereinafter referred to as an "SHG element"), and an output mirror 55, all disposed on an optical axis 50. A coating for high reflection of a solid-state laser fundamental wave is applied to the LD 51 side end face of the solid-state laser rod 53, and an optical resonator 56 is constituted in cooperation with the output mirror 55. The solid-state laser rod 53 is excited by an output light beam 501 from the LD 51 and generates a fundamental wave 502. The fundamental wave 502 thus generated resonates so as to pass through the SHG element 54 and is converted into a second harmonic 503. The second harmonic 503 passes through the output mirror 55 and is output to the exterior. For example, if, in this conventional example, Nd:YAG is used as the solid-state laser rod 53 and KTiOPO.sub.4 (hereinafter abbreviated to "KTP") is used as the SHG element, then it is possible to obtain as the second harmonic a green laser beam having a wavelength of 532 nm.
Next, an example of a conventional sum frequency generating solid-state laser system will be described below with reference to FIG. 6.
The sum frequency generating solid-state laser system comprises an LD 61 disposed on an optical axis 60, a condenser lens 62, a sum frequency generating non-linear optical element 63 (hereinafter referred to as an "SFG element"), a solid-state laser rod 64, and an output mirror 65. A coating for high reflection of a solid-state laser fundamental wave is applied to the LD 61 side end face of the SFG element 63, and an optical resonator 66 is constituted in cooperation with the output mirror 65. An output light beam 601 from the LD 61 passes through the SFG element 63 and excites the solid-state laser rod 64. A fundamental wave 602 generated from the solid-state laser rod 64 resonates so as to pass through the SFG element 63, and in the SFG element 63 fundamental wave 602 is mixed with the output light beam from the LD 61 to generate a sum frequency radiation 603. The sum frequency radiation 603 passes through the solid-state laser rod 64 and the output mirror 65, and then, is output to the exterior. For example, if in this conventional example Nd:YAG is used as the solid-state laser rod 64 and KTP is used as the SFG element 63, it is possible to obtain as the sum frequency a blue laser beam having a wavelength of 459 nm. The crystallographic axes of the KTP used in the sum frequency generating solid-state laser and of the second harmonic generating KTP, relative to the optical axis, are disposed in such directions as to generate a sum frequency radiation and a second harmonic, respectively.
According to the prior art, however, in the case where both a second harmonic and a sum frequency radiation are required, it is necessary to separately provide a second harmonic generating solid-state laser system and a sum frequency generating solid-state laser system, resulting in an increased number of parts and an increased size of the entire system, thus leading to an increased cost. It has also been necessary to make adjustment for alignment with respect to both the second harmonic generating solid-state laser system and the sum frequency generating solid-state laser system.